1. Field of the Invention
The present invention relates to communicating in a wireless communication system and, more particularly, to an apparatus and method for controlling access to a network by mobile terminals.
2. Description of the Related Art
A universal mobile telecommunication system (UMTS) is a European-type, third generation IMT-2000 mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM). UMTS is intended to provide an improved mobile communication service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
In December 1998, a Third Generation Partnership Project (3GPP) was formed by the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea. The 3GPP creates detailed specifications of UMTS technology. In order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created within the 3GPP for standardizing the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the standard specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN 20), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 illustrates an exemplary basic structure of a general UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a terminal or user equipment (UE) 10, a UTRAN 20, and a core network (CN) 30.
The UTRAN 20 includes one or more radio network sub-systems (RNS) 25. Each RNS 25 includes a radio network controller (RNC) 23 and a plurality of Node-Bs (base stations) 21 managed by the RNC 23. The RNC 23 handles the assignment and management of radio resources and operates as an access point with respect to the core network 30.
The Node-Bs 21 receive information sent by the physical layer of the terminal 10 through an uplink, and transmit data to the terminal 10 through a downlink. The Node-Bs 21 operate as access points of the UTRAN 20 for the terminal 10.
The UTRAN 20 constructs and maintains a radio access bearer (RAB) for communication between the terminal 10 and the core network 30. The core network 30 requests end-to-end quality of service (QoS) requirements from the RAB, and the RAB supports the QoS requirements the core network 30 has set. Accordingly, by constructing and maintaining the RAB, the UTRAN 20 can satisfy the end-to-end QoS requirements.
The services provided to a specific terminal 10 are roughly divided into the circuit switched (CS) services and the packet switched (PS) services. For example, a general voice conversation service is a circuit switched service, while a Web browsing service via an Internet connection is classified as a packet switched (PS) service.
For supporting circuit switched services, the RNCs 23 are connected to the MSC 31 of the core network 30 and the MSC 31 is connected to the GMSC 220 that manages the connection with other networks. For supporting packet switched services, the RNCs 23 are connected to the SGSN 35 and the GGSN 37 of the core network 30. The SGSN 35 supports the packet communications with the RNCs 23 and the GGSN 37 manages the connection with other packet switched networks, such as the Internet.
The 3GPP system can provide multimedia broadcast multicast service (MBMS). The 3GPP TSG SA (Service and System Aspect) defines various network elements and their functions required for supporting MBMS services. A cell broadcast service provided by the conventional system is limited to a service in which text type short messages are broadcast to a certain area. The MBMS service is a more advanced service that multicasts multimedia data to terminals (UEs) 10 that have subscribed to the corresponding service in addition to broadcasting multimedia data. An example of MBMS service includes news channels, music channels, movie channels, etc.
The MBMS service is a downward-dedicated service that provides a streaming or background service to a plurality of terminals 10 by using a common or dedicated downward channel. The MBMS service is divided into a broadcast mode and a multicast mode.
The MBMS broadcast mode facilitates transmitting multimedia data to every user located in a broadcast area, whereas the MBMS multicast mode facilitates transmitting multimedia data to a specific user group located in a multicast area. The broadcast area signifies a broadcast service available area and the multicast area signifies a multicast service available area.
Users who desire to receive the MBMS service first receive a service announcement provided by a network. The service announcement provides the terminal 10 with a list of services to be provided and related information. In addition, the users must receive a service notification provided by the network. The service notification provides the terminal 10 with information related to the broadcast data to be transmitted.
If the user intends to receive the multicast mode MBMS service, the user subscribes to a multicast subscription group. A multicast subscription group is a group of users who have completed a subscription procedure. Once a user has subscribed to the multicast subscription group, the user can join a multicast group to receive a specific multicast service. A multicast group is a group of users that receive a specific multicast service. Joining a multicast group, also referred to as MBMS multicast activation, means merging with the multicast group that has users who wish to receive the specific multicast service. Accordingly, the user can receive the specific multicast data by joining a multicast group (i.e., MBMS multicast activation).
The RNC 23 transfers the MBMS user data to the terminal 10 through the base station (Node-B) 21 via the user plane of the UTRAN protocol. The UTRAN 20 transfers the MBMS user data by constructing and maintaining a radio access bearer (RAB) for a call communication between the terminal 10 and the core network 30. The MBMS user data is transferred only by downlink. The MBMS radio bearer facilitates transferring, only to a specific terminal 10, the user data of a specific MBMS service transferred by the core network 30 to the UTRAN 20.
The MBMS radio bearer is divided into a point-to-multipoint type and a point-to-point type. The UTRAN 20 selects one of the two types of MBMS radio bearers to provide the MBMS service. To select one of the two MBMS radio bearers, the UTRAN 20 should recognize the number of users (terminals 10) of a specific MBMS service existing in one cell.
The UTRAN 20 may count the number of terminals to determine the type of MBMS radio bearer. The UTRAN 20 informs the terminals that it is counting the number of terminals when it provides information about the MBMS service via a MBMS common control channel or performs paging for a specific MBMS service group.
When a terminal 10 receives a service notification of an MBMS service indicating that counting is being performed on the corresponding service, the terminal establishes a connection between an RRC entity of the terminal 10 and an RRC entity of the UTRAN 20 by transferring an RRC connection request message to the UTRAN through an uplink common channel. The RRC connection request message informs the UTRAN that the terminal desires to receive the corresponding MBMS service.
By counting the number of terminals 10 that have transferred an RRC connection request message, the UTRAN 20 can recognize users who desire to receive the specific MBMS service in one cell. The UTRAN 20 then sets up an MBMS radio bearer on the basis of the count.
If the number of users existing in a corresponding cell is smaller than a certain threshold value, the UTRAN 20 sets a point-to-point MBMS radio bearer. If the number of users existing in a corresponding cell is greater than or equal to a certain threshold value, the UTRAN sets a point-to-multipoint MBMS radio bearer. However, the conventional paging method through which the UTRAN 20 recognizes the number of terminals 10 that desire to receive an MBMS service has the shortcomings.
When the UTRAN 20 performs the MBMS service notification, response messages, such as RRC response messages, are sent from terminals 10 that desire to receive the MBMS service. The response messages are simultaneously concentrated at uplink channel, resulting in an increase in interference and load on the uplink. Because the UTRAN 20 performs the MBMS service notification to the plurality of terminals 10 using the MBMS common control channel and the corresponding terminals 10 simultaneously inform the UTRAN 20 that they want to receive the corresponding MBMS service through the uplink common channel both the interference and load on the uplink increases.
Because the interference and load increases, an undesirably long period of time may be required for the terminals 10 to send response messages. For this reason, some terminals may fail to transmit the response message by the time when then UTRAN 20 should set up the MBMS radio bearer.
Once the UTRAN 20 receives a number of response messages from the terminals 10 that is above the threshold for setting up the MBMS point-to-multipoint radio bearer up to, the UTRAN does not need to receive any additional response messages because all requirements for selecting the radio bearer have been met. However, in the conventional art, even if the UTRAN 20 has already received above a threshold number of response messages, the UTRAN continues to receive response messages up until the MBMS radio bearer is set. Therefore, uplink radio resources are undesirably wasted.